1. Field of the Invention
This invention relates generally to blind signal separation, and in particular to blind down conversion of multiple co-channel and adjacent channel radio frequency (RF) signals into separate baseband signals with low crosstalk and suppression of interference.
2. Description of the Related Art
Wireless voice and data communication products and services have experienced tremendous growth in popularity in recent years, leading to spectral congestion and interference. Interference may be caused by multiple communication signals on a single channel, generally referred to as co-channel interference, or by communication signals on adjacent channels or networks. Such spectral congestion and interference have typically resulted in temporary short-term service problems or outages. However, as competition for services increases and customer satisfaction becomes more critical, such service outages, even if temporary, will no longer be tolerated and technical solutions to increase network capacity and improve robustness to interference are therefore desirable.
Another concern for existing communication networks is the need to offer increased data rates. For many existing networks, one solution is the implementation of a Quality-of-Service (QoS) facility, whereby users can be assigned multiple data channels according to communication resource requirements, dependent upon a software application currently being used on a wireless mobile communication device (“mobile device”), for example. For mobile devices, processing multiple data channels is difficult to implement using known designs without significantly increasing hardware complexity, power dissipation and size.
These problems were identified as early as the 1980's, and significant research has since been conducted. These efforts have focused primarily on modifying known radio receivers by adding a spatial filter or beamformer (See for example R. T. Compton Jr., Adaptive Antennas: Concepts and Performance, Prentice Hall, Englewood Cliffs, N.J., 1988, and R. Monzingo and T. Miller, Introduction to Adaptive Arrays, Wiley and Sons, New York, 1980). More recently, methods based on the statistical independence of source signals have been developed. In both cases, spatial information obtained using an array antenna is exploited. However, array antenna size and associated receiver complexity and high power consumption prevent widespread implementation of such techniques.